As is known in the art, there are a variety of circuits that limit the energy in a circuit. For example, dimming circuits for lighting applications adjust the brightness of a light source. Exemplary power control, dimming, and/or feedback circuits are shown and described in U.S. Pat. Nos. 5,686,799, 5,691,606, 5,798,617, and 5,955,841, all of which are incorporated herein by reference.
However, known power control/dimmer circuits typically have significant performance degradation for non-linear loads. Some known circuits have feedback from the load that can generate significant Electromagnetic Conductive interference (EMC), which degrades circuit performance and limits use of the feedback.
FIG. 1 shows an exemplary prior art dimming circuit 10 having a diac D coupled to a triac TR gate. A resistor R and a potentiometer P are coupled as shown. A black wire terminal BLK is coupled to the resistor R and the triac TR and a white wire terminal WH is coupled to the load LD, which is coupled to the potentiometer P and the triac TR, as shown.
As shown in FIG. 2, when the voltage across the potentiometer P reaches a predetermined level VT, the diac D fires and the triac TR enables the circuit to become conductive. An input signal IS has a conductive region CR and non-conductive region NCR based upon when the diac fires.
While this circuit arrangement may be effective for linear loads, non-linear loads may render the circuit unstable. In addition, storage capacitors and other energy storage devices will charge to a voltage level corresponding to the peak Vp of the input signal. That is, the non-linear load selects the charge voltage level. In addition, current surges are not generated at optimal times and can degrade circuit performance.
It would, therefore, be desirable to overcome the aforesaid and other disadvantages.